NICKEL-TITANIUM ENDODONTICINSTRUMENTSHistory: In 1960, the superelastic property of nickel-titanium alloy, also known as Nitinol, was discovered by Buehler and Wang at the US Naval Ordnance aboratory! "he name Nitinol was derived from the elements that make up the alloy, nickel and titanium, and #nol$ for the Naval Ordnance aboratory!"he trademark Nitinol refers specifically to the first nickel-titanium wire marketed for orthodontics!In 197, %iv&an suggested the use of nickel '() by weight *'(-Nitinol+ in the fabricationof files , corrosion-resistant root canal points to replace silver points!In 19!!, Walia reported the first use of nickel titanium in endodonticsNumber -. files fabricated from nickel-titanium orthodontic alloy were shown to have two or three times the elastic fle/ibility in bending and torsion, as well as superior resistance to torsional fractures, compared with No!-. stainless steel files manufactured by the sameprocess! "he results suggested that Nitinol files might be promising for the instrumentation of curved canals!In 199" *0ay+, Serene introduced these new files to students in the %ollege of1ental 0edicine at the 0edical University of South %arolina! ater these and other similar files became available to the profession generally!S#$%r%l&sti'ity:"he superelasticity of nickel titanium, the property that allows it to return to its original shape following significant deformation, differentiates it from other metals, such as stainless steel, that sustain deformation and retain permanent shape change! "hese properties make nickel-titanium superior than stainless steel files concerning2 3le/ibility! %onformation of canal curvature! 3racture resistance! Wear resistance!4lloys such as nickel titanium, that show superelasticity, undergo a stress-induced martensitic transformation from a parent structure, which is austenite! On release of the stress, the structure reverts back to austenite, recovering its original shape in the process!11eformations involving as much as a -() strain can be completely recovered in these materials, as compared with a ma/imum of -) in conventional alloys!"he superelastic behavior of nickel titanium also occurs over a limited temperature window! 0inimum residual deformation occurs at appro/imately room temperature! 4 composition consisting of .( atomic percent nickel and .( atomic percent titanium seems ideal, both for instrumentation and manufacture!M&n#(&'t#r%: A-H&n) instr#*%nts:1ifferent designs2 5 style, 6edstrom, 3le/-7, 8-double fluted, S-double fluted, U files, anddrills, spreaders and pluggers! +-Rot&ry instr#*%nts:Nickel-titanium was allowed to be used in rotary instrumentation due to2Nickel-titanium instruments are better than stainless steel instruments in machining dentin, wear resistance *Kazemi and Spngberg 1996)! With the ability to machine flutes, radial lands *U shape design+ have become available! 7adial lands allow nickel-titanium files to be used as reamers in a 9'( degree motion as opposed to the traditional reamers with more acute rake angles! 4lthough the most common use of this new design has been as a rotary file, the identicalinstrument is available as a hand instrument! :n addition, a converter handle is available that allows the operator to use the rotary file as a hand instrument!0oreover, new prototype rotary motors now offer the potential for improved tor;ue control with automatic reversal that decrease rotary instrument breakage!+io'o*$&ti,ility:Nickel-titanium files are biocompatible and appear to have e/cellent anticorrosive properties *Serene 1995).Torsion&l Str%n-t. &n) S%$&r&tion:Nickel-titanium files were found to be less resistant to fracture than stainless steel files! 4lthough both metals meet or e/ceed 4NS:!2"he nickel titanium?s superelasticity does not mean its high torsional strength! "his misconception has led to unnecessary file breakage when first using this new metal! Wolcott and 6imel-@@A showed that there is no significant difference between ma/imum tor;ue and tor;ue at failure for stain less steel files, whereas the nickel-titanium instruments showed a significant difference between ma/imum tor;ue and tor;ue at failure i!e! the time between #windup$ and fracture in nickel-titanium instruments is e/tended, which could lead to a false sense of security!%anal curvature and the number of rotations determined file breakage! Separation occurs at the point of ma/imum curvature of the shaft! So it would be wise to know that nickel-titanium instruments are safer when used passively!Ni'/%l-Tit&ni#* 0r%'tions &n) 0r%1%ntion12 I( r%sist&n'% is %n'o#nt%r%): Stop immediately, increase the coronal taper and negotiate additional length, using a smaller, (!(= taper stainless steel hand file! "hese instruments re;uire a passive techni;ue, otherwise fracture will occur!"2 C&n&ls t.&t 3oin &,r#$tly &t s.&r$ &n-l%s2 "he straighter of the two canals should first be enlarged to working length and then the other canal, only to where they &oin! :f not, a nickel-titanium file may reverse its direction at this &uncture, bending backon itself and damaging the instrument!42 C#r1%) '&n&ls t.&t .&1% & .i-. )%-r%% &n) s*&ll r&)i#s o( '#r1&t#r%2 *over '( degrees and found 9 to B mm from working length+ 52 Instr#*%nt (&ti-#%: 3iles should not be overused! On'% only is the safest number #better safe than sorry$!3actors affecting the number of file use2-- 1egree of canal calcification and curvature2 calcified , curved canal stresses the file more than an uncalcified , straight canal! =- Use of lubricants2 decreases stresses!9- 1egree of operator skill!- L%)-%s2 Nickel-titanium should not be used to bypass ledges! Only & s*&ll '#r1%) st&inl%ss st%%l file should be used! edges allow space for deflection of a file! "he nickel-titanium instrument can then curve back on itself36- T%%t. 6it. 7S8-ty$% '#r1%s2 Should be approached with caution , ade;uate (l&rin- o( t.% 'oron&l t.ir) to .&l( of thecanal!7- I( t.% rot&ry instr#*%nt is $ro-r%ssin- %&sily in & '&n&l 9 t.%n (%%ls &s i( it .its ,otto*: 1O NO" 4CCD 411:":ON4 C7ESSU7EF "his will cause the instrument tip to bind theninstrument breakage! :n this situation, remove the instrument and try a smaller, (!(= taper hand instrument, *either stainless steel or nickel-titanium+ carefully flaring and enlarging the uninstrumentedapical portion of the canal!!- Tot&l or (ri'tion&l (it o( t.% (il% in t.% '&n&l:4void cutting with the entire length of the file blade2 "his will cause the instrument to lock!On removal from the canal, the debris should appear on the middle portion of the file only!"he tip and coronal section of the file should not carry debris!E/cept for2a! Negotiating calcified canals!b! Enlarging the apical portion of the canal!c! "he use of the Buchanan G" file!:f this occurs, rotate the instrument in a counterclockwise direction and remove it from the canal and taper of coronal one-third of the canal is increased! Nickel-titanium instruments with tapers from (!(B, (!(', and greater, as well as Gates-Glidden drills and sonic